1. Field of the Invention
This invention relates to method and device for detecting deflection amount of ink jets in an ink jet printer wherein ink drops are continuously discharged from a nozzle or nozzles to effect printing by means of the ink drops. More particularly, this invention relates to method and device suitable for use in an ink jet printer of multi-nozzle type wherein a plurality of nozzles are disposed substantially perpendicular to the direction of deflection of flying ink drops, whereby printing speed is elevated.
2. Description of the Prior Art
In a conventional ink jet printer, ink is pressurized by a pump so that the ink is jetted from a nozzle. In this mechanism, however, there is a case of causing such a disadvantage that load applied to the pump fluctuates because of change in viscosity of the ink due to temperature, decrease in filterable area of a filter due to continuous use, etc. so that the rate of discharge for the ink becomes fluctuated. Theoretically, the deflection amount of ink drops is determined by deflection force of electrostatic field in the flying course of the ink drops and a rate of discharge of the ink from a nozzle. Therefore, fluctuation in load with respect to the pump brings about variation in the deflection amount of the ink drops, causing the distortion in the printed image.
Accordingly, in such a conventional ink jet printer, fluctuation in the deflection of the ink drops has been reduced by such a manner that the deflection is detected from time to time and driving force of the pump is subjected to feedback control on the basis of the detected result. As a method for detecting the deflection, such a method has heretofore been adopted in which change induced in an electric conductor by the charge ink drop is converted into voltage. In the above method, however, occurrence of various disadvantages could not be avoided particularly to an ink jet printer of multi-nozzle type wherein a plurality of nozzles are disposed substantially perpendicular to a direction of the deflection.
More specifically, in the above-mentioned method, when applied to the multi-nozzle type ink jet printer, either a plurality of sensors for detecting the deflection amount are arranged in a row in respect to the respective nozzles, or a single sensor is provided for only any one nozzle among the above nozzles. In the former case, since the sensor has a large dimension of several tens millimeters, it is difficult to use such large sensors in the multi-nozzle type printer where a distance between nozzles cannot be kept so broad. On the other hand, in the latter case, since the conditions of the nozzles other than the sensor-provided nozzle cannot be known, it is required to reduce error among the nozzles by maintaining the dimensions of all the nozzles and charging electrodes uniform. Thus, the manufacture of these nozzles ahd charging electrodes are difficult.